<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    
</body>
</html>

<script>
    function jisuanqi(){
        var a=Number(prompt("请输入第一个数字"));
        var op=(prompt("请输入运算符"));
        var b=Number(prompt("请输入第二个数字"));
        return { '+':a+b, '-':a-b, '*':a*b, '/':a/b }[op];
    }
    alert(jisuanqi());
</script>